Abstract : This document describes an optical relay system for bringing a Cassegrain-type or other type telescope infrared image through a mount elevation axis, yoke and azimuth axis for focusing at an image plane on the mount which is stationary relative to compound motion of the telescope. The relay system is made up or of deflecting or folding mirrors, apertured flat mirrors and concave spherical and elliptical mirrors arranged for minimizing field degradation of off-axis objects. (Author)